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Refactoring Database Access in Marauroa: Difference between revisions

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imported>Hendrik Brummermann
imported>Kymara
 
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At the moment databaseDatabase access in marauroa iswas designed for a single thread application. While this does workworks most of the time in turn based games (yes, Stendhal is turnedturn based internally), it prevents doing non time critical stuff in another thread. In Stendhal we have the problem that any update or delete operation to the gameEvents table that takes more than a couple of seconds, kills the server.
 
== Requirements ==
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== Design ==
 
<!-- OUTDATED [[Image:Marauroa.server.game.db.png]] -->
 
== Concept FAQ ==
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=== Where did IDatabase / JDBCDatabase go? ===
 
It was replaced by smaller classes specializedspecializing onin one task each. They can be found in the package <code>marauroa.server.game.db</code> endingand they end with "DAO".
 
=== What are those new ...DAO classes? How do they work? ===
 
TheyDAO arestands for "data access object". The basic idea is, and has been from the start, that the database related code is not in the original classes but at some central point outside the game logic. This used to be JDBCDatabase, but one single class for all database operations is very unhandyhard to maintain. So JDBCDatabase has been splittedsplit into a number of small classes focused on one area each: AccountDAO, CharacterDAO, GameEventDAO...
 
These classes replace the old IDatabase / JDBCDatabase and do the database stuff. All of their methods have two signatures: One with gets ana DBTransaction object as first parameter and one without. This is for your convenience: In most cases it those functions are not part of a larger context so you do not have to care about transactions at all because: the DAO-classes do the transaction handling on their own. There are, however, a small number of cases in which you want to do multiple calls to DAOs in one single transactionstransaction. In this case you get a DBTransaction from the TransactionPool and provide it as first parameter to DAO-methods. After you are done you must either commit or rollback your changes with the appropriate methods in the class TransactionPool.
 
=== I have extended the JDBCDatabase class. How does this work with DAOs? ===
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DAO classes should never be instantiated directly. Instead you should (and marauroa does) use the DAORegistry. This allows you to write a subclass of a DAO provided by marauroa and register it instead. If you are familiar with Spring, this is a similar concept. But without all the bulk of xml configuration files, parameter injection and interfaces with only one single implementation.
 
Imagine you want to subclass the CharacterDAO with your class SomeGameCharaterDAOSomeGameCharacterDAO:
<source lang="java">
public class SomeGameCharacterDAO extends CharacterDAO {
...
</source>
 
You simply register it as
<source lang="java">
DAORegistry.get().register(CharacterDAO.class, new SomeGameCharaterDAO());
DAORegistry.get().register(CharacterDAO.class, new SomeGameCharacterDAO());
Note: In the register call the first parameter is the parent clase you want to replace.
</source>
Note: In the register call the first parameter is the parent class you want to replace.
 
 
=== What are those database adapters for? ===
 
TheThey are a thin layer of database abstraction. This allows us to not only support MySQL but also database systems withwhich don't require an external server.
 
 
=== Why is there a method getLastInsertId? ===
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=== What happened to Transaction, JDBCTransaction, Accessor, JDBCAccess? ===
 
They wherewere replaced with DBTransaction. You can get a DBTransaction from the TransactionPool. Make sure that you commit or rollback it after use.
 
=== What happendhappened to JDBCSQLHelper and StringChecker? ===
 
They have been moved to marauroa.server.db
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Please have a look at the ...DAO classes in the marauroa.server.game.db package and split your sub class accordingly. After that is done you need to register them in the DAORegistry with the class of the original DAO and an instance of your class.
 
 
== Porting of JMaPacman ==
 
The following diff shows the complete list of changes that were required to port JMaPacman. I think it may help you to get a feeling on how to adjust your own code.
<!--
Don't use syntax highlighting here because it does not work well with the diff characters and bold formation
<source lang="java">
-->
public class MaPacmanRPRuleProcessor implements IRPRuleProcessor
{
public AccountResult createAccount(String username, String password, String email) {
- IDatabase database = DatabaseFactory.getDatabase();
+ '''TransactionPool transactionPool = TransactionPool.get();'''
- Transaction trans = database.getTransaction();
+ '''DBTransaction trans = transactionPool.beginWork();'''
+ '''AccountDAO accountDAO = DAORegister.get().get(AccountDAO.class);'''
try {
- trans.begin();
- if (database.hasPlayer(trans, username)) {
+ if ('''accountDAO'''.hasPlayer(trans, username)) {
return new AccountResult(Result.FAILED_PLAYER_EXISTS, username);
}
- database.addPlayer(trans, username, Hash.hash(password), email);
+ '''accountDAO'''.addPlayer(trans, username, Hash.hash(password), email);
- trans.commit();
+ '''transactionPool.commit(trans);'''
return new AccountResult(Result.OK_CREATED, username);
} catch (SQLException e1) {
- try {
- trans.rollback();
- } catch (SQLException e2) {
- //logger.error("Rollback failed: ", e2);
- System.out.println("Rollback failed: " + e2);
- }
+ '''transactionPool.rollback(trans);'''
return new AccountResult(Result.FAILED_EXCEPTION, username);
}
}
public CharacterResult createCharacter(String username, String character, RPObject tmpl) {
- IDatabase database = DatabaseFactory.getDatabase();
+ '''TransactionPool transactionPool = TransactionPool.get();'''
- Transaction trans = database.getTransaction();
+ '''DBTransaction trans = transactionPool.beginWork();'''
+ CharacterDAO characterDAO = DAORegister.get().get(CharacterDAO.class);
try {
- trans.begin();
- if (database.hasCharacter(trans, username, character)) {
+ if ('''characterDAO'''.hasCharacter(trans, username, character)) {
return new CharacterResult(Result.FAILED_PLAYER_EXISTS, character, tmpl);
}
@@ -196,18 +190,13 @@
- database.addCharacter(trans, username, character, object);
+ '''characterDAO'''.addCharacter(trans, username, character, object);
- trans.commit();
+ '''transactionPool.commit(trans);'''
return new CharacterResult(Result.OK_CREATED, character, object);
} catch (Exception e1) {
//logger.warn("SQL exception while trying to create a new character: ", e1);
- try {
- trans.rollback();
- } catch (SQLException e2) {
- //logger.error("Rollback failed: ", e2);
- System.out.println("Rollback failed: " + e2);
- }
+ '''transactionPool.rollback(trans);'''
return new CharacterResult(Result.FAILED_EXCEPTION, character, tmpl);
}
}
 
 
[[Category:Marauroa]]
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